The al-Qa'ida claim, which could not be independently verified, linked the deadly blasts to the war in Iraq, calling Amman the "backyard garden" for US operations. Jordan became a target because it was "a backyard garden for the enemies of the religion, Jews and crusaders...a filthy place for the traitors...and a centre for prostitution."

The claim of responsibility, signed in the name of the spokesman for al-Qa'ida in Iraq, said the attacks put the United States on notice that the "backyard camp for the crusader army is now in the range of fire of the holy warriors.

The attacks ­ two of which were on upper-range hotels frequented by foreign tourists, businessmen and international officials ­ ended several years in which, despite a series of foiled bombings, the Jordanian capital had seemed almost immune from the violence in the region surrounding it.

The almost simultaneous bombings shortly before 9pm came at the Grand Hyatt, the Radisson SAS, which was popular with Israelis and many other international tourists, and the Days Inn hotel.

The Jordanian Deputy Prime Minister, Marwan Muasher, said that 57 had been killed in the blasts. Abu Musab al-Zarqawi, held responsible for a series of suicide bombings and kidnappings in Iraq, was identified as a key suspect by both Mr Muasher and an unnamed US counter-terrorism official.

The claims are perhaps inevitable given al-Zarqawi's origins in Jordan and the fact the attacks bore the hallmarks of others attributed to him.

Jordanian police spokesman Major Bashir al-Da'aja said: "There were three terrorist attacks on the Grand Hyatt, Radisson SAS and Days Inn hotels and it is believed that the blasts were suicide bombings."

Jordan's interior minister, Awni Yarfas, who was at the Radisson hotel, told reporters: "There were explosions in the Hyatt and the Radisson ... Yes, they were bombs."

What appears to have been the first bomb, at 8:50pm local time, struck the Grand Hyatt, completely shattering the stone entrance. One reporter said he saw at least seven bodies removed from the hotel and many more wounded carried out on stretchers.

At the Radisson, where up to 250 people had been attending a wedding reception, at least five were killed and at least 20 wounded. Police sources told Reuters that the blast had been caused by a bomb placed in a false ceiling. Security sources speculated that a nearby bar was the target, rather than the wedding party itself.

The country's King Abdullah II condemned the bombings and said "justice will pursue the criminals".

The King, who was on an official visit to Kazakhstan, cut short his trip and started back for home last night after issuing a statement carried by the official Jordanian news agency Petra which described the attacks as " criminal acts committed by a deviant and misleading bunch" which would not sway Jordan from continuing "its battle against terrorism".

The UN secretary general, Kofi Annan, cancelled a planned visit to Jordan today because of the bombings.

Police set up roadblocks round the hotels, causing traffic chaos in the normally busy streets of Amman. In a unconfirmed report, the US television network CNN quoted an eyewitness as saying the Jordanian prime minister's car was at the Grand Hyatt at the time of the blast.

One of the wedding guests at the Radisson, who gave his name only as Ahmed said: "We thought it was fireworks for the wedding but I saw people falling to the ground. I saw blood. There were people killed. It was ugly."

An American businessman who also declined to give his name said he was at the Grand Hyatt when the explosion occurred, and that a "bomb went off in the lobby". A British guest at the same hotel said: "It was a miracle that we made it out without a scratch."

The capital itself has long seemed one of the most peaceful in the Arab world, but militants fired three Katyusha rockets at a Navy ship docked at Aqaba this August, narrowly missing it and killing a Jordanian soldier. Jordanian officials blamed that attack on al-Qa'ida elements from Iraq.

Before the US invasion of Iraq, Amman attracted anti-Saddam exiles. Many other Iraqis have taken refuge there since the collapse of the dictator's regime.

Despite a fall-off in tourism since the beginning of the Israeli-Palestinian conflict Jordan has striven to exploit exceptional tourist attractions including the ancient Nabatean city of Petra, the desert landscape of Wadi Rum, the Red Sea resort of Aqaba the Byzantine mosaics of Madaba, and the Roman forum and amphitheatre of Amman.

While there were no immediate reports of Israeli casualties, Israel arranged a rare night-time opening of the Allenby Bridge across the Jordan river to allow tourists to return to Israel.